Time COUNT iterations of CODE. CODE may be a string to eval or a code reference; either way the CODE will run in the caller's package. Results will be printed to STDOUT as TITLE followed by the times. TITLE defaults to "timethis COUNT" if none is provided. STYLE determines the format of the output, as described for timestr() below.

The COUNT can be zero or negative: this means the minimum number of CPU seconds to run. A zero signifies the default of 3 seconds. For example to run at least for 10 seconds:

timethis(-10, $code)

or to run two pieces of code tests for at least 3 seconds:

timethese(0, { test1 => '...', test2 => '...'})

CPU seconds is, in UNIX terms, the user time plus the system time of the process itself, as opposed to the real (wallclock) time and the time spent by the child processes. Less than 0.1 seconds is not accepted (-0.01 as the count, for example, will cause a fatal runtime exception).

Note that the CPU seconds is the minimum time: CPU scheduling and other operating system factors may complicate the attempt so that a little bit more time is spent. The benchmark output will, however, also tell the number of $code runs/second, which should be a more interesting number than the actually spent seconds.

Returns a string that formats the times in the TIMEDIFF object in the requested STYLE. TIMEDIFF is expected to be a Benchmark object similar to that returned by timediff().

STYLE can be any of 'all', 'none', 'noc', 'nop' or 'auto'. 'all' shows each of the 5 times available ('wallclock' time, user time, system time, user time of children, and system time of children). 'noc' shows all except the two children times. 'nop' shows only wallclock and the two children times. 'auto' (the default) will act as 'all' unless the children times are both zero, in which case it acts as 'noc'. 'none' prevents output.

FORMAT is the printf(3)-style format specifier (without the leading '%') to use to print the times. It defaults to '5.2f'.

Arguments: TIME is the minimum length of time to run CODE for, and CODE is the code to run. CODE may be either a code reference or a string to be eval'd; either way it will be run in the caller's package.

TIME is not negative. countit() will run the loop many times to calculate the speed of CODE before running it for TIME. The actual time run for will usually be greater than TIME due to system clock resolution, so it's best to look at the number of iterations divided by the times that you are concerned with, not just the iterations.

If the Time::HiRes module has been installed, you can specify the special tag :hireswallclock for Benchmark (if Time::HiRes is not available, the tag will be silently ignored). This tag will cause the wallclock time to be measured in microseconds, instead of integer seconds. Note though that the speed computations are still conducted in CPU time, not wallclock time.

April 04-07th, 1997: by Jarkko Hietaniemi, added the run-for-some-time functionality.

September, 1999; by Barrie Slaymaker: math fixes and accuracy and efficiency tweaks. Added cmpthese(). A result is now returned from timethese(). Exposed countit() (was runfor()).

December, 2001; by Nicholas Clark: make timestr() recognise the style 'none' and return an empty string. If cmpthese is calling timethese, make it pass the style in. (so that 'none' will suppress output). Make sub new dump its debugging output to STDERR, to be consistent with everything else. All bugs found while writing a regression test.